<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .pie {
      width: 100px;
      height: 100px;
      border-radius: 50%;
      background: red linear-gradient(to right, red 50%, blue 0);
    }
    .pie:before {
      content: '';
      display: block;
      margin-left: 50%;
      height: 100%;
      background: red;
      border-radius: 0 100% 100% 0 / 50%;
      transform-origin: left;
      transform: rotate(.5turn);
    }
    .pie2 {
      border-radius: 100%;
      width: 300px;
      height: 300px;
      background-image: conic-gradient(#f66 0 25%, #66f 25% 30%, #f90 30% 55%, #09f 55% 70%, #3c9 70% 100%);
    }
  </style>
</head>
<body>
  <div class="pie"></div>
  <div class="pie2"></div>
</body>
</html>
